The present invention relates to a thermoplastic resin composition comprising a polyester and polypropylene, and more particularly to a thermoplastic resin composition comprising a polyester and polypropylene extremely compatible with each other.
Polypropylene resins have excellent moldability, chemical resistance, water resistance, etc., but they are poor in mechanical properties such as flexural modulus, impact resistance, etc. To improve such properties of the polypropylene resins, attempts have been made to blend the polypropylene resins with polyesters having excellent impact resistance, mechanical strength, etc.
However, since the polypropylene and the polyester do not have good compatibility, proposals have been made to add a modified polyolefin which is grafted with an unsaturated carboxylic acid or its anhydride to improve their compatibility.
Japanese Patent Laid-Open No. 60-58447 discloses a thermoplastic resin composition comprising (A) polypropylene, (B) a thermoplastic polyester, (C) a modified propylene-.alpha.-olefin random copolymer, (D) a hydrogenated styrenebutadiene block copolymer, and (E) an inorganic filler, the modified propylene-.alpha.-olefin random copolymer (C) being produced by grafting a propylene-.alpha.-olefin random copolymer (G) having a crystallization degree of 0 to 30 weight % measured by X-ray analysis and a propylene content of 50 to 70 mol % with 0.01 to 5 weight % of a graft monomer selected from unsaturated carboxylic acids or their derivatives, the component (C) being 1 to 80 parts by weight, the component (D) being 1 to 50 parts by weight, and the component (E) being 5 to 150 parts by weight, per 100 parts by weight of the total of components (A) and (B).
Also, various proposals have been made to add epoxy group-containing copolymers as compatibilizers to the thermoplastic resin compositions of polypropylenes and polyesters.
Japanese Patent Laid-Open No. 61-60744 discloses a thermoplastic resin composition comprising (A) 10-90 weight % of polypropylene, (B) 90-10 weight % of a saturated polyester resin, and (C) 2-30 parts by weight, per 100 parts by weight of the polypropylene (A)+the saturated polyester resin (B), of an epoxy group-containing copolymer.
Japanese Patent Laid-Open No. 61-60746 discloses a thermoplastic resin composition comprising (A) 50-90 weight % of a polypropylene resin selected from a modified polypropylene and a modified polypropylene/polypropylene composition; (B) 50-10 weight % of a saturated polyester resin; and (C) 2-30 parts by weight, per 100 parts by weight of the polypropylene resin (A)+the saturated polyester resin (B), of an epoxy group-containing copolymer.
However, these thermoplastic resin compositions fail to show sufficiently improved flexural modulus and impact resistance. In addition, since sufficient compatibility of the polypropylene with the polyester cannot be achieved, the resulting thermoplastic resin compositions are likely to suffer from surface peel.